In June, law enforcement authorities in Chişinău, the Moldovan capital, received an email from a parent reporting that their child had been kidnapped. Police and prosecutors traced the message to the kidnapper, a skill that is becoming essential in an increasingly digital age.

Thankfully, it was only a training exercise. The UN Office on Drugs and Crime (UNODC) visited Moldova, the poorest country in Europe, at the request of authorities there, who were ill-equipped to deal with an increase in cybercrime and internet-based human trafficking.

UNODC provided three days of training in basic forensic techniques, such as tracing a criminal across the internet and finding images and other information on a locked computer.

"[It's] old-fashioned detective work in a digital age," Adam Palmer, a senior expert in cybercrime and emerging crimes at UNODC, told IPS.

Though official figures on human trafficking are notoriously hard to come by due to the crime's secretive nature, the International Labour Organisation estimates that 21 million people worldwide are forced into labour, including 4.5 million victims of forced sexual exploitation.

With the pressure of emerging technologies, anti-trafficking organisations, as well as law enforcement agencies, need to adapt their knowledge of new techniques and devices used by criminals. Smartphones are a new phenomenon; a couple of years ago the majority of crimes were being committed on desktop computers, Palmer said. "Now, nearly every crime seems to have some kind of phone involved in it."

But the problem of internet-based sex trafficking – the use of the web for the recruitment, advertisement and sale of people, overwhelmingly women – is not confined to Moldova. It is also an issue in developed countries including the US.

Amy Fleischauer, director of victim services at the International Institute of Buffalo, a group that helps immigrants and refugees settle in western New York state, has found survivors of sex and labour trafficking being recruited and advertised via the internet. The institute spends time with survivors so they know how easily they can be tracked through Facebook, GPS on their phones and their internet history.

It is important to realise the relationship between sex and labour trafficking, Fleischauer said. She described a number of cases involving agricultural workers in the US, where brothels were established on farms to "satisfy workers". "Sex trafficking almost always involves labour trafficking," Fleischauer said, "focusing on just sex trafficking does a disservice to victims."

Increased awareness of trafficking through the internet has caught the attention of companies that run the web, and whose products are being used to facilitate the crime. "The most effective way to investigate cybercrime is … to work with private sector companies," Palmer said, pointing out that companies were willing to help, as traffickers were abusing their technology.

Jacquelline Fuller, director of giving at Google, said the company had a "longstanding interest" in helping to combat child exploitation and trafficking over the internet. "More recently, we took a deep dive to see … how we could help," she said.

Bradley Myles has seen first hand the changing face of sex trafficking. The chief executive of Polaris Project, a US-based non-profit that works directly with survivors of human trafficking, Myles told IPS that from 2005 to 2008, Craigslist was one of the worst channels for internet-based sex trafficking. After Craigslist removed many of the advertisements that led to women and girls being exploited.

The extent of internet-based trafficking is unknown, according to Fleischauer, but increased awareness and getting police better educated on types of cases, recruitment and strategies could help. "I think we have no idea what's out there," she said.